Introduction to the iPod Touch. iPod Touch This is the iPod Touch!
TOUCH
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Transcript of TOUCH
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TOUCH
PSYCHOPHYSIOLOGY
L. Négyessy PPKE, 2010
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Haptic exploration of local shape
Static stimuli
1-2 mm 2,8 mmmin. 0,5 mm: 3%
0,17 mm
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Thresholds I
Braille dots’ height: 500 µm
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6 x 18 = 108 blunt pins
230 Hz
Vibrating stimuliOPTACON
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Thresholds II
Discriminabitlity (d’) of complex waveformsfor low frequencies
d’
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The 4 channel model- psychophysics
Threshold
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Sensory Afferents
Conduct.: 35-70 m/s(Hand scan: 60-80 mm/s)
The 4 channel model- neurophysiology
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Receptive field organization (finger pad)
SAI RA P SAII?
RF size 1 mm2 0.82 mm2 diffuse diffuse
Aff. denz. 100 cm-2 150 cm-2 350/ finger ? (low)
Diverg.(RF area)
4-16(5 mm2)
4-16 (5 mm2)
1:1 1:1
Converg. 1:1 2-7 1:1 1:1
Adequ. stim. Strain energy density (point, edge, curve)
Slip, load force
High freq. vibration
Skin stretch
function Form, texture Grip control, fine
discr.
Distant events, tool use
Hand shape
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Form perception:dots, edges, curves
Braille readingAperiodic grating
SAI channel
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Receptive field characteristics relevant to form perception
RAI & SAI channels
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Surround supression
skin mechanics
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Perception of texture:roughness
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Fine texture perception: SAI spatial variation*
*Mean absolute difference in firing rates between SAI afferents with RFs separated by ~2mm
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SAI spatial variation code for fine textures (0.2-1mm)
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Summary of form & texture perception
coding of spatial features Evidences of SA1 specialization for the representation of
spatial information: SA1 responses to stimulus elements on a surface are
independent of the force of application. SA1-receptive fields grow minimally (relative to RA receptive
fields) with increasing indentation depth. SA1 afferents possess a response property, surround
suppression, which confers response properties similar to those produced by surround inhibition in the central nervous system. This response property is a consequence of sensitivity to strain energy density, not a synaptic mechanism.
SA1 spatial resolution is affected minimally by changes in scanning velocity at velocities up to at least 80 mm s–1.
SA1 afferents are at least ten times more sensitive to dynamic than to static stimuli.
SA1 responses to repeated skin indentation are practically invariant: the variability is about one impulse per trial regardless of the number of action potentials evoked.
The RA system has greater sensitivity but poorer spatial resolution and limited dynamic range.
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Vibrotactile perception:flutter, vibration
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RA channel
Periodic StimulusFiring rate
Periodic StPeriodicity (IS interval)
Aperiodic StFiring rate
Periodic+aperiodic St Only firing rate
firing rate periodicity
monkey
ideal obs.
Thresholds ratios: psychometric/neurometric thresholds
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P channel
10 nm skin motion at 200 Hz
ideal obs.
of St motion
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Response to vibrating stimulus
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P channel intense filtering (at nearly 60 dB per decade) of low-frequency
stimuli respond to stimuli less than 100–150 Hz with a phase-locked,
Poisson discharge, therefore a whole population firing randomly but at a rate proportional to the instantaneous stimulus amplitude can represent the stimulus waveform accurately
RA channel RA neurons of S1, like their afferent fibers, fire periodically, in
phase with mechanical oscillations RA neurons modulate their firing rates as a function of the
stimulus frequency Flutter is encoded by firing rate of RA neurons
Summary of vibrotactile perception- coding of temporal features
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AdaptationPeripheral mechanisms
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Time course of adaptation and recovery
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RA interference in spatial processing
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Tool use
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Coding object size
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Grasping and manipulation
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Grasping and manipulation
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SUMMARY
•The 4 channel model of vibrotactile discrimination•RF correlates of the 4 channel model•Elements of form perception•Texture (roughness) perception•Vibrotactile perception•Object manipulation